1. Field of the Invention
The invention relates to a novel process for the preparation of bicyclic amidines by reaction of lactones with primary amines. The invention also relates to novel bicyclic amidines having functional groups, especially amino, hydroxyl and/or mercapto groups, and to their use as catalysts for the preparation of polyurethanes.
2. Background Art
Bicyclic amidines are strong organic bases which, owing to their high basicity coupled with low nucleophilicity and their ready solubility in almost all solvents, have found numerous applications. Particularly well-known bicyclic amidine compounds are those commonly referred to by the abbreviations DBN and DBU, i.e., 1,5-diazabicyclo[4.3.0]non-5-ene (2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidine) and 1,8-diazabicyclo[5.4.0] undec-7-ene(2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine), respectively.
A review of the uses of these compounds in chemical syntheses can be found, for example, in Synthetica Merck, Volume II, E. Merck, Darmstadt, (1974), pp. 118-119 and 124.
A known process for preparing bicyclic amidines starts from N-(.omega.-aminoalkyl)lactones which, when heated with acidic catalysts, undergo cyclization with elimination of water to form the amidines (German Patent No. C 1,545,855). The N-(.omega.-aminoalkyl)lactones are obtained, for example, from the corresponding cyano compounds by hydrogenation; in particular, for example, N-(.gamma.-aminopropyl)pyrrolidone is obtained from N-(.beta.-cyanoethyl)-pyrrolidone [see, e.g., W. Reppe et al., Justus Liebigs Ann. Chem., 596, (1955), p.211]. It is also possible to prepare N-(.omega.-aminoalkyl)lactones from the corresponding lactones and .alpha.,.omega.-diaminoalkanes (German Patent No. C 730,182). The known processes for the preparation of bicyclic amidines have the disadvantage that they include at least two synthesis steps with working up of the intermediates.
It is known that bicyclic amidines are highly suitable as catalysts for the preparation of polyurethanes (French Patent No. 1,542,058). A considerable disadvantage of this use, however, is that bicyclic amidines are not firmly bonded within the polyurethane formed and therefore, over time, diffuse out of or are extracted from the polyurethane. In each case there is unnecessary pollution of the environment.